Wireless communication systems often employ power amplifiers for increasing the power of a signal. In a wireless communication system, a power amplifier is usually the last amplifier in a transmission chain (the output stage) and it is the amplifier stage that typically demands the most attention to power efficiency. High gain, high linearity, stability, and a high level of power-added efficiency (i.e., the ratio of the difference between the output power and the input power to DC power) are characteristics of an ideal amplifier.